The Convention on Road Signs and Signals, commonly known as the Vienna Convention on Road Signs and Signals, is a multilateral treaty designed to increase road safety and aid international road traffic by standardising the signing system for road traffic (road signs, traffic lights and road markings) in use internationally.

Amendments, including new provisions regarding the legibility of signs, priority at roundabouts, and new signs to improve safety in tunnels were adopted in 2003.

Both the Vienna Convention and the Geneva Protocol reflected a common consensus on road traffic signs that evolved primarily in Europe in the mid-20th century. Most jurisdictions outside Europe have not adopted either treaty, and maintain their own systems of road traffic signals. For example, the U.S. Manual on Uniform Traffic Control Devices (MUTCD) does not follow the symbol policy espoused by the Vienna Convention; for example signs for speed limits and forbidden parking are among the most visible differences. In order to make it accepted in as many countries as possible, the convention allows some variations, for example danger warning signs can be triangular or square diamond in shape and road markings can be white or yellow.

An alternative convention called the SADC-RTSM, provided by the Southern African Development Community, is used by 10 countries in southern Africa. Many of the rules and principles of the SADC-RTSM are similar to those of the Vienna Convention.

It also specifies the symbols and pictograms which may be used, and the orientations in which they may be used. When more than one is available, the same one must be used nationally. All signs, except for those that do not apply at night, must be reflective enough to be seen in darkness with headlights from a distance.

The convention also specifies road markings. All such markings must be less than 6 mm high, with cat's eye reflectors no more than 15 mm above the road surface. The road markings shall be white or yellow.[3]

The length and width of markings varies according to purpose, although no exact figures for size are stated; roads in built up areas should use a broken line for lane division, while continuous lines must only be used in special cases, such as reduced visibility or narrowed carriage ways.

All words painted on the road surface should be either of place names, or of words recognisable in most languages, such as "Stop" or "Taxi".

The priority is determined by Priority Route or Yield signs or if none of the above regular right of way rule.

Red flashing lights may only be used at the locations specified above; any other use of the lights is in breach of the convention. Red lights must be placed on top when lights are stacked vertically, or on the side closest to oncoming traffic if stacked horizontally.

The only countries in Europe that are not signatories to the Convention are Ireland, Andorra, Malta, the United Kingdom, and Liechtenstein. Iceland, Spain, and the Holy See are all signatories but have yet to ratify the Convention.

The only countries in Asia that are not signatories to the Convention are Bangladesh, Malaysia, Republic of China (Taiwan), People's Republic of China (including Hong Kong and Macau), Japan, Israel, Palestine, Saudi Arabia, Jordan, Lebanon, Syria, Armenia, Yemen, Oman, North Korea, and Afghanistan.

Cambodia, Indonesia, Laos, South Korea, and Thailand are all signatories, but have yet to ratify the Convention.